Jue D. Wang The Molecular Interface of Replication Elongation and the Cellular Environment Accurate DNA replication is essential for the survival and fitness of all organisms. Replication is believed to be regulated mostly during initiation. The central hypothesis of this proposal is that there also exist extensive regulatory mechanisms that control DNA replication even after initiation and possibly throughout elongation. My recently discovery of a novel regulatory mechanism of replication elongation by a small molecule established a precedent for such mechanisms. I plan to greatly expand this theme to include a spectrum of other small molecules and protein regulators. I propose that these regulators form a multifaceted interface between replication and other cellular processes. Through this interface, replication elongation can respond readily to metabolic and external cues; conversely, cells can monitor the replication status and respond accordingly. I have developed novel genomic tools to monitor aspects of replication in vivo that could not be observed before. Using these tools, I will define the nature of changes in replication elongation status under different conditions and study how it affects the choice of the cellular responses. I will then use metabolic and replication profiling to test the hypothesis that multiple small molecules induced by a spectrum of stresses regulate replication elongation robustly. Finally, using proteomic approaches, I plan to find protein factors that couple replication with other cellular processes, and examine their roles in regulating elongation and detecting replication stress. These studies will be carried out in model bacteria but will be extended to higher organisms in the future. Our ultimate goal is to expand the existing paradigm of replication control to include extensive post-initiation regulatory mechanisms. The factors identified in our study are likely to play paramount roles in the maintenance of genome stability and prevention of genetic diseases and cancer.